The ability to differentiate between positive and negative environmental stimuli is critical to an animal's survival. However, the neural circuits that endow the brain with the ability to differentiate positive and negative motivationally significant stimuli have been difficult to disentangle and represent one of the most important fundamental neuroscience questions today. The development and application of optogenetic approaches has allowed us to probe the causal relationships between activity in specific circuit elements and animal behavior relevant to psychiatric disease states such as anxiety, addiction and depression. In this seminar, Kay Tye will discuss her research on the corticolimbic circuits that mediate valence processing.